1. Field
One or more embodiments relate to microfluidics, and more particularly, to a valve unit controlling fluid flow, a microfluidic device including the same, and a method of fabricating the valve unit.
2. Description of the Related Art
In general, microfluidic devices are used to perform biological or chemical reactions by manipulating small amounts of fluid. Microfluidic devices include microfluidic structures arranged in a platform in various forms, such as chips, disks, or the like. Such a microfluidic structure includes a chamber that can accommodate a fluid, a channel through which the fluid can flow, and a valve that can control the flow of the fluid. The chamber, channel, and valve may be disposed in the platform in a variety of configurations.
A biochip is such a microfluidic structure that is arranged in a small-sized chip platform in order to perform tests including biochemical reactions. In particular, a device that is manufactured to perform multi-step processing and manipulation on a single chip, is referred to as a lab-on-a chip.
To transfer a fluid in a microfluidic structure, an operating pressure is needed. A capillary pressure or a pressure applied by a separate pump is used as the operating pressure. Recently, centrifugal force-based microfluidic devices in which a microfluidic structure is arranged in a compact disk (CD)-shaped platform have been proposed. These devices are also referred to as Lab CD or Lab-on a CD.
An example of a valve unit included in a microfluidic device is disclosed in U.S. Patent Application Publication No. 2008/0042096. The valve unit includes an injection hole for injecting a phase transition material into the microfluidic device. To form the injection hole in the microfluidic device, which is an injection product, a protrusion corresponding to the injection hole has to be formed in a mold. A resin injected into the mold is separated from each other by the protrusion and then rejoined, which can cause a so-called weld-line formed in the injection product after the resin is cured. The weld-line deteriorates the rigidity of the microfluidic device, resulting in defects. In addition, it is difficult to smoothly polish the mold due to the protrusion formed in the mold. Thus, a surface of the injection product becomes rough and the smoothness thereof deteriorates. In addition, a process of closing the injection hole is further needed after forming the valve unit, and thus the manufacturing costs increase. Moreover, due to a draft angle formed in the protrusion in order to easily separate the injection product from the mold, an inclination is formed in an inner circumferential surface of the injection hole. As a result, the injection product has a step difference such that when the valve is operated by applying energy, such as electromagnetic waves, the step difference of the injection hole may cause diffusion of light. Thus, an operation of the valve unit may be interfered with and malfunction.